Multilayered wall especially consisting of gossamer-type inflatable structures

ABSTRACT

A multilayer wall includes Gossamer-type rigidifiable and inflatable structures, the wall including a layer of a composite material that can be rigidified by polymerisation, and is flanked, on the inside, by a gas-impermeable layer, and, on the outside, by at least one anti-adhesion and protection layer. The multilayer wall is characterised in that the external layer is partially permeable to gas and impermeable to liquid or viscous phases of the matrix of the composite material.

The present invention pertains more particularly to structures commonly called Gossamer, which are ultralightweight deployable space structures.

Generally, when objects are sent into space, there is little room available under rocket nosecones or in shuttlecraft cargo bays. Therefore, these objects must be made compact, and they must be deployed as soon as they are in orbit. The best known example of such structures is that of solar panels.

These deployments are made today by means of mechanical systems that can be complex, taking into account the difficult conditions of the spatial environment.

Regardless of the deployment technology implemented, it is fundamental to control the geometry of the deployed object, since this is generally a key element of its functioning, for example, in the case of radio antennas or solar panels.

One of the difficulties encountered in controlling this deployment is associated with the vacuum in space. In fact, the structures are obviously assembled on the Earth, at atmospheric pressure, and during their transport into orbit, they must undergo depressurization. This depressurization is accompanied by gas flow that can deform the structures or disrupt their deployment, if these flows are not controlled.

The present invention pertains more particularly to structures called Gossamer, of the multilayered wall inflatable type that can be made rigid.

Such a wall comprises a layer of composite material that can be made rigid, made up of a polymerizable pre-impregnated fabric, a gastight layer positioned on the inside of the multilayered deployable structure to permit its inflation and, on the outside, at least one layer that assures protection and preventing the layer of composite material from sticking to itself when the structure is folded to be packed in its container, which will be placed in the rocket or the shuttle.

In such structures, it is of prime importance to assure that no residual gas is imprisoned during manufacture and/or folding does not persist after depressurization. This can, in fact, be prejudicial to its good deployment in orbit.

It is necessary, in fact, to control deployment so that it is done according to the desired geometry and with sufficient regularity, taking into account the surrounding systems and the situation of weightlessness.

The object of the invention is to permit, notably during the depressurization phase, the evacuation of air imprisoned between the different layers of a multilayered wall of Gossamer-type inflatable structures that can be made rigid.

For this purpose, the subject of the invention is a multilayered wall, notably of Gossamer-type inflatable structures that can be made rigid, said wall comprising a layer of composite material that can be made rigid by polymerization, flanked on the inside with a gas-tight layer, and on the outside with at least one protective and anti-stick layer, characterized in that said outer layer is partially permeable to gases and impermeable to the liquid or viscous phases of the matrix of said composite material.

According to one embodiment, said outer layer comprises one or more parts that are permeable to gases and impermeable to liquid or viscous phases of the matrix of said composite material.

Said gas-permeable parts, impermeable to other fluids, are advantageously formed by vents, made up of holes created in said layer and covered with a membrane of a material that permits the free circulation of gases, while preventing the passage of the liquid or viscous phase of the matrix of said composite material, said membrane being placed onto said outer layer and joined together with the latter with the possible aid of an appropriate means, the cumulative surface of said membrane that allows gas passage being determined in order to assure a rapid depressurization of the inside of the multi-layered wall.

Advantageously, the membrane is of a material that is not wettable by the composite material resin, and is preferably a microporous membrane of expanded polytetrafluoroethylene.

The membranes are assembled and fastened, for example by gluing, by means of a silicone-type adhesive.

By way of illustrative example, the thickness of the membrane is of the order of several hundred micrometers, typically of the order of 300 micrometers.

Other characteristics and advantages will arise from the description that follows of vent embodiments according to the invention, a description given solely by way of example and relative to the attached drawing, in which:

FIG. 1 is a schematic section of a multilayered wall of an inflatable structure that can be made rigid;

FIG. 2 represents an embodiment of the multilayered wall according to the invention,

FIG. 3 illustrates the arrangement of vents according to the invention on a foldable structure, and

FIG. 4 is a depressurization curve for a multilayered structure conforming to the invention.

In FIG. 1, one wall of a Gossamer-type multilayered structure that can be deployed by inflation and made rigid is shown schematically in section.

This laminated structure comprises a central layer 1 of composite material formed by means of a layer of fibers pre-impregnated with a resin appropriate for rigidization of the structure in orbit once it has been deployed. The rigidization is conducted according to one of the technologies commonly used in these circumstances and which have been enumerated, for example, in the article “Recent advances in rigidization of Gossamer structures”, from the ECCOMAS study entitled “Recent Advances in Textile Membranes and Inflatable Structures” pages 1-19, SPRINGER Publ., BERLIN, GERMANY.

Composite material 1 is coated, on the inside of the inflatable structure, with a thin and gastight film 2, for example, a polyimide film.

The polyimide family is a family of materials known for their high mechanical properties and excellent electrical properties, their resistance to high temperatures, their low absorption of humidity, their good inflation gas-barrier property and their chemical stability.

Aromatic polyimides, notably the material known under the tradename KAPTON®, are particularly appropriate for creating film 2.

The outside of the inflatable structure of composite material 1 is coated with a film 3, for example, also of polyimide (notably an aromatic polyimide), for protecting the composite material and preventing this material from sticking to itself when the inflatable structure is folded prior to placement in the smallest possible space in its launch container. Film 3 also participates in the shaping of the deployable structure by making up a “molding matrix”, as it were.

Multilayered structure 1, 2, 3 is kept in place during its manufacture and handling by the sticky nature of the central layer 1 of composite material.

During deployment by inflation of structure 1, 2, 3, which is conducted in vacuum, it is very desirable, for reasons of regularity and precision of deployment of the structure, to evacuate as much as possible any residual gas bubbles that can persist in the space between the two layers 2 and 3 surrounding composite material 1, the presence of these residual gases being inevitable, since sandwich 1, 2, 3 is made and folded on Earth.

Conforming to the invention, outer layer 3 is provided with at least one vent, and preferably several, each made up of a hole 4 created in film 3, in a given area of the surface of this film, and covered, as illustrated by FIG. 2, with a membrane 5 placed and fastened onto film 3.

Holes 4 can be any shape whatever, but round is preferred since this is the easiest and has the best mechanical strength.

Membranes 5 are simple disks, for example circular, of a diameter slightly greater than that of holes 4.

The disks are made by stamping out from a thin film 3 of a material that can let gases pass, as illustrated by arrows 6 (FIG. 2) inside the space between films 2 and 3 and toward the outside of the multilayered wall.

The thickness of membrane-disks 5 is of several hundred micrometers, for example, of the order of 300 micrometers.

In contrast, the material of disks 5 must not permit diffusion out of the multilayered wall of the liquid or viscous formulation of the matrix of composite 1, which would pollute the deployed structure.

Preferably, membrane-disks 5 are attached by gluing.

A material suited for making up disks 5 is expanded polytetrafluoroethylene and especially one of the materials sold under the tradename MIKROTEX® of the MIKROPULL Company or under the tradename GORE-TEX® of the W.L. Gore & Associates company, and preferably materials of the HPM series, whose microporosity is very suitable, since the pores are not sealed by the composite material resin; such a material is not wettable by the resin and also is very suited to gluing onto a polyimide-type material by means of a silicone glue 7 positioned in a ring around the periphery of each membrane 5.

The section of holes 4 and their number depends on the desired air flow rate, the objective being to obtain a rapid depressurization of the order of several tens of seconds.

The location of vents (4, 5), depends on the shapes, dimensions and methods of folding of the deployable structures.

In FIG. 3, by way of example, a repetitive pattern 8 of a known accordion folding mode of a tubular structure is shown. In this hexagonal pattern 8, two holes 4 are provided, positioned symmetrically, each covered with a membrane 5. The position of the vents is preferably optimized.

Here, the number of vents is associated with the volume of gas to be evacuated.

With regard to positioning, the vents are positioned so as to limit the flow path of gas molecules, i.e., in the four zones of hexagonal pattern 8, and also in each zone “isolated” by folding, i.e., in those places where the folds can locally render the product gastight, and to create zones between which gases cannot circulate.

FIG. 4 shows a depressurization profile as a function of time of a multilayered structure according to the invention.

In the test thus illustrated, an almost complete depressurization is obtained, passing from 1 bar to 0.05 bar in a time lapse of 90 seconds, which is considered completely satisfactory. It is observed that depressurization is not only rapid, but also relatively regular, which certainly contributes to the harmonious deployment of the inflatable structure.

It is to be noted that the invention can also be applied to multilayered walls with a central layer of composite material interposed between two gastight layers, which can be used in contexts other than the creation of Gossamer structures requiring the presence of a composite material without bubbles, at least one of the two gastight layers being provided with the vent device according to the invention. 

1. A multilayered wall, notably for Gossamer-type inflatable structures that can be made rigid, said wall comprising a layer of composite material that can be made rigid by polymerization, flanked on the inside with a gastight layer, and on the outside with at least one protective and anti-stick layer, wherein said outer layer is partially permeable to gases and impermeable to the liquid or viscous phases of the matrix of said composite material.
 2. The multilayered wall according to claim 1, wherein said outer layer has one or more parts permeable to gases and impermeable to the liquid or viscous phases of the matrix of said composite material.
 3. The multilayered wall according to claim 2, wherein said parts are vents made up of holes created in said layer and covered with a membrane of a material permitting free circulation of gases while preventing passage of the liquid or viscous phase of the matrix of composite material, said membrane being placed onto said outer layer and joined to this layer possibly by means of an appropriate attachment means, the cumulative surface that is capable of gas passage being determined so as to assure a rapid depressurization of the inside of multilayered wall.
 4. The multilayered wall according to claim 3, wherein said membrane is of a material that cannot be wetted by the resin of composite material.
 5. The multilayered wall according to claim 4, wherein said membrane is a microporous membrane of expanded polytetrafluoroethylene.
 6. The multilayered wall according to claim 5, wherein said membrane is made up of material sold under the tradename GORE-TEX®, series HPM.
 7. The multilayered wall according to claim 3, wherein said outer layer is of polyimide.
 8. The multilayered wall according to claim 7, wherein the polyimide is an aromatic polyimide.
 9. The multilayered wall according to claim 8, wherein the aromatic polyimide is KAPTON®.
 10. The multilayered wall according to claim 3, wherein said membrane is fastened by gluing.
 11. The multilayered wall according to claim 10, wherein said gluing is carried out with silicone glue.
 12. The multilayered wall according to claim 3, wherein said membrane has a thickness of the order of several hundred micrometers.
 13. The multilayered wall according to claim 12, wherein said membrane has a thickness of the order of 300 micrometers. 